public class MyLinkedList {
    static class ListNode{
        public ListNode prev;
        public ListNode next;
        public int val;
        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode head;
    public ListNode last;

    public void creatList(){
        ListNode node1 = new ListNode(12);
        ListNode node2 = new ListNode(23);
        ListNode node3 = new ListNode(34);
        ListNode node4 = new ListNode(45);
        ListNode node5 = new ListNode(56);
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;
        this.head = node1;
        this.last = node5;
    }
    public int size(){
        ListNode cur = head;
        int count = 0;
        while (cur != null){
            count++;
            cur = cur.next;
        }
        return count;
    }
    public void display(){
        ListNode cur = head;
        while (cur != null){
            System.out.print(cur.val +  " ");
            cur = cur.next;
        }
        System.out.println();
    }

    public boolean contains(int index){
        ListNode cur = head;
        while (cur != null){
            if (cur.val == index){
                return  true;
            }
            cur = cur.next;
        }
        return false;
    }

    public void addFirst(int val){
        ListNode next;
        ListNode prev;
        ListNode node = new ListNode(val);
        if (head != null){
            node.next = head;
            head.prev = node;
            head = node;
        }else {
            head = node;
            last = node;
        }
    }

    public void addLast(int val){
        ListNode node = new ListNode(val);
        if (head == null){
            head = node;
            last = node;
        }else {
            last.next = node;
            node.prev = last;
            last = last.next;
        }
    }

    public ListNode search(int index){
        ListNode cur = head;
        while (index != 0){
            cur = cur.next;
            index--;
        }
        return cur;
    }
    public void addIndex(int data,int index){
        if (index < 0 || index > size()){
            throw new no("位置不合法");
        }
        if (index == 0){
            addFirst(data);
        }
        if (index == size()){
            addLast(data);
        }
        ListNode cur = search(index);
        ListNode node = new ListNode(data);
        node.next = cur;
        cur.prev .next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }



}
